<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        td{
            padding: 5px 85px 5px 85px;
            text-align: center;
        }
        select,button,option,input{
            vertical-align:middle;
            margin-bottom: 1px;
        }
        select,button,option{
            height: 25px;
        }
        input{
            height: 19px;
        }

    </style>
</head>
<body>
<form>
    <select>
        <option value="美元">美元</option>
    </select>
    <button name="exchange" value="exchange">互换</button>
    <select>
        <option value="美元">美元</option>
    </select>
    金额：<input name="num" value="num">
    <button name="cul" value="cul">按汇率计算</button><br>

    <table border="1">
        <tr style="background-color: red">
            <th colspan="3">
                按当前汇率换算结果
            </th>
        </tr>
        <tr>
            <td>美元</td>
            <td>汇率</td>
            <td>人民币</td>
        </tr>
        <tr>
            <td>100</td>
            <td>7</td>
            <td>700</td>
        </tr>
    </table>
</form>
</body>
</html>